Many means for improving on-ice performance (braking ability on ice) of studless tires have been proposed. For example, known techniques include blending a hard foreign material or hollow particles in the rubber, and forming micro-irregularities on the surface of the rubber, thereby removing the water film produced on the surface of ice to improve frictional force on ice (for example, see Japanese Unexamined Patent Application Publication No. H11-35736). Other methods include reducing the content of reinforcing filler in the rubber composition to increase flexibility, or blending a special compounding agent that forms holes in the rubber and absorbing water on an icy road surface to increase adhesive properties between the rubber and ice, thereby improving friction force.
However, when hollow particles, for example, are blended in rubber, there is a problem that cavities form in the tread rubber and wear resistance decreases.